(1) Field of the Invention
The present invention relates to a multi-component glass doped with microparticles, used as a material for sharp cut filter, a material for infrared-transmitting filter, a nonlinear optical material, etc., as well as to a process for producing said glass. More particularly, the present invention relates to a multi-component glass doped with microparticles comprising crystallites of CdS.sub.x Se.sub.y Te.sub.z (0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, 0.ltoreq.z.ltoreq.1, x+y+z=1), as well as to a process for producing said glass.
(2) Description of the Prior Art
Glasses doped with microparticles of CdS, CdSe, CdTe, CdS.sub.x Se.sub.1-x solid solution (0&lt;x&lt;1), CdS.sub.x Se.sub.1-(x+y) Te.sub.y solid solution (0&lt;x&lt;1, 0&lt;y&lt;1, 0&lt;x+y&lt;1) or the like are in use as a material for sharp cut filter having an absorption end at the wavelength range of visible light or at an infrared range, or as a material for infrared-transmitting filter. In recent years, glasses doped with microparticles of CdS.sub.x Se.sub.1-x have been found to show third-order nonlinear properties [J. Opt. Soc. Am. Vol. 73, No. 5, pp. 647-653 (1983)] and are drawing attention as a nonlinear optical material for optical switch, optical computer, etc.
Such glasses doped with microparticles are, in general, multi-component glasses produced by a melting process comprising (a) heat-melting a mixture consisting of a starting material to become a matrix of a desired glass and a starting material to become microparticles dispersed in the matrix, to obtain a glass melt, (b) cooling the glass melt to room temperature to obtain a glass comprising a matrix and elements which are to constitute microparticles dipsersed in the matrix and which are dissolved as ions in the matrix, and (c) heating the glass from room temperature to a given temperature and heat-treating the glass at the same given temperature to precipitate microparticles in the matrix.
When a glass doped with microparticles is produced by the above conventional melting process, however, there occurs, in the step of heat-treating raw materials to obtain a glass comprising a matrix and elements which are to constitute microparticles dispersed in the matrix, vaporization of said elements to be dissolved as ions in the matrix, particularly chalcogen elements such as S, Se, Te and the like (the chalcogen elements do not include oxygen in this specification). The concentration of chalcogen element ions in glass cannot be increased even by using, in the material mixture, an increased amount of the material to become microparticles. Therefore, the concentration of the microparticles precipitated in the matrix by heat treatment is usually less than 3% by weight.
As a result, a thin sharp cut filter or an infrared-transmitting filter produced from a multi-component glass doped with microparticles obtained by the convention melting process, has tended to show mild (not sharp) rise in the light absorption curve, and it has been difficult to obtain a sharp cut filter or an infrared-transmitting filter both having good spectral characteristics and yet being lightweight. Further, since the third-order optical susceptibility (.sub.X.sup.(3)) which is a yardstick for the degree of third-order nonlinearity, is proportional to the concentration of microparticles, it has been difficult to obtain a multi-component glass doped with microparticles, having excellent third-order nonlinearity by the conventional melting process.